We are having the same problem:
TypeError: o is null
Reuploading advanced-custom-fields-pro solved the error.
We have problems with the values returned as well.
We’ve defined an image field and set it to return an “Image-Array”. The value that gets returned is the ID, no matter what was chosen in the field editor.
We have the exact same problem. We are using flex content with wysiwyg and some other fields and the backend is unusable. Scrolling will kill the browser. There is a serious issue with the JS in the ACF version. We are using pro btw.
Could the developers please have a look at this.
At the moment, the plugin is not scalable for bigger, more complex environments. We would love to use ACF for future projects, but this really concerns me.